1. Field of the Invention
This invention relates to key depression detection apparatuses that detect depressing operations of keys (or key depressions) in keyboard instruments such as acoustic pianos and electronic keyboard instruments.
2. Description of the Related Art
In acoustic pianos, vibrations of strings are transmitted to soundboards to cause sound radiation (or emission). Pianos having silencing functions use sensors for detecting operations of keys and operations of hammers interlocked with keys, based on which musical tone signals are correspondingly produced. Operators (e.g., users and players) may use headphone sets to listen to musical tones corresponding to amplified musical tone signals, so that they can enjoy playing pianos and the like without disturbing their neighborhoods.
Acoustic pianos may include grand pianos, upright pianos, and the like. In the case of a grand piano, for example, three strings are stretched under tension and tuned with respect to each of middle pitch sounds and high pitch sounds, so that the three strings are simultaneously struck by a single hammer upon depression of a key. When an operator depresses a soft pedal, an action (or a keyboard assembly) interlocked with a key is slightly shifted in position in a key arrangement direction (i.e., a horizontal direction or operator's left-hand-right-hand direction), so that a hammer strikes only two strings among three strings to lessen tone volume. The action is supported on a keybed by means of a keyboard frame, which is one type of a key frame for mounting the action interlocked with the key and which performs reciprocating motion being interlocked with the soft pedal in the key arrangement direction. In order to smoothly perform such operation, the aforementioned keyboard frame has a specific structure using a frame member extending in a direction perpendicular to the key arrangement direction.
Grand pianos having silencing functions are equipped with key depression detection apparatuses incorporating photo-interrupters, which operate in cooperation with plate-like key shutters arranged for keys and which are attached to sensor cases fixed to keyboard frames. In this apparatus, upon depression of a key, a key shutter is activated to block light, the magnitude of which may be correspondingly varied and is sensed by a photo-interrupter to detect an operation of the key, thus generating a musical tone signal. The sensor case is used to determine positions of holding sensors; therefore, it should be subjected to specific positioning accurately in correspondence with an arrangement of keys. In an assembling operation of a piano, it takes a relatively long time for work to carefully set positioning with respect to the sensor case. In particular, the position of a sensor case should be strictly restricted by the position of a keyboard frame having the aforementioned structure. Therefore, it is required for workers to use specific tools and to appropriately set different holes for arrangements of different keyboard frames whose dimensions differ from each other.
Silencing structures can be additionally arranged for the existing grand pianos to realize silencing functions thereafter. In this case, it is required for workers to arrange silencing structures in consideration of designs and specifications of pianos respectively; therefore, it may take a relatively long time for work to arrange sensor cases appropriately in the existing pianos.
Upright pianos can be designed to realize silencing functions by using key depression detection apparatuses incorporating photo-interrupters that operate in cooperation with key shutters arranged for keys and that are attached to sensor cases fixed to keybeds (or key frames), for example. In this case, sensor cases are used to determine positions of holding sensors, so that they should be subjected to specific positioning accurately in correspondence with arrangements of keys. Therefore, in an assembling operation of a piano, it takes a relatively long time for work to set appropriate positioning with respect to a sensor case.
Silencing structures can be additionally arranged for the existing upright pianos thereafter. In this case, it is required for workers to arrange silencing structures in consideration of designs and specifications of pianos respectively; therefore, it may take a relatively long time for work to arrange sensor cases appropriately in the existing pianos.
Other types of keyboard instruments such as electronic keyboard instruments having electronic sound sources also use key depression detection apparatuses incorporating sensors that operate in cooperation of keys and that are attached to sensor cases. In this case, it is required for workers to set specific positioning with respect to sensor cases accurately in correspondence with arrangements of keys. In an assembling operation of such an electronic keyboard instrument, it takes a relatively long time for work to set specific positioning with respect to the sensor case.